The present invention relates generally to scroll compressors and, more particularly, to a method and apparatus for electrochemically machining a matched set of scroll members for use in such compressors, thereby ensuring proper sealing between respective wrap surfaces of the scroll members during compressor operation.
A typical scroll compressor comprises two scroll members, each having an involute wrap, wherein the respective wraps interfit to define a plurality of closed compression pockets. When one of the scroll members is orbited relative to the other, the pockets decrease in volume as they travel between a radially outer suction port and a radially inner discharge port, thereby conveying and compressing the refrigerant fluid
It is generally believed that the scroll-type compressor potentially offers quiet, efficient and low maintenance operation in a variety of refrigeration system applications. However, several design and manufacturing problems persist. For instance, the operating efficiency of a compressor depends upon the integrity of axial and radial sealing between the scroll members. One type of leakage that can occur is between compression pockets of the scroll compressor at those locations where the wrap walls sealingly contact each other to define the boundaries of the moving compression pockets. Leakage between the wraps themselves or between the tips of the wraps and the opposing scroll base plates reduce the efficiency and capacity of the compressor.
Conventional scroll machine practice has been to use a numerically controlled profiling machine, or NC machine, to cause a milling tool and workpiece to undergo relative movement according to mathematical equations descriptive of an intended or desired involute curve. However, deviations of the milling cutter from the desired involute path occur due to errors in the movement of the machine caused by constantly changing forces against the two cartesian axes and time lags in the servo response of the drive motor. Further, this type of milling machine uses rotating end mills that potentially cause a swirl finish on the scroll wraps and wrap tips. This swirl finish, caused by an incorrectly ground or worn milling head, creates an uneven finish that causes a distinctive leak path over the scroll wrap tip, thereby reducing compressor efficiency. High tooling costs are also associated with using such complex milling machinery.
A previous solution to the leakage problem was to "wear in" the scroll wraps one to another. In this system, the compressor would operate until the scroll wrap surfaces wear to the point where they are in constant contact and mate perfectly. A drawback to this solution is that it may take literally days of wear in time per compressor to achieve the needed leakproof seal between the matched scroll wraps. It is undesirable to require compressor purchasers to wear in the compressors they purchase. Further, there is no feasible way of constructing and operating a production factory to contain thousands of operating scroll compressors just to wear in the scrolls.
Various types of wrap finishing have also been utilized to prevent and reduce the leak paths between the scrolls. Conventional thought has been to increase the smoothness of the scroll wear surfaces to that of almost a mirror like finish. Electroplating, deburring, and ultrasonic leveling systems have been utilized to construct smooth wrap surfaces and edges. These current wrap finishing processes are expensive and require a long cycle time to produce.
The present invention is directed to overcoming the aforementioned problems associated with prior methods of manufacturing scroll members for use in scroll compressors, wherein it is desired to create a matched set of fixed and orbiting scroll members without requiring an extended run-in time for the compressor by the use of electrochemical machining (ECM).
Electrochemical machining is a process of shaping and removal of metal from a work piece by an electrochemical process utilizing an external current source and a flow of electrolyte between a work tool and a work piece to be shaped. Metal removal from the scroll members is effected by the process of ionizing a conductive electrolyte between the scrolls thereby dissolving metal atoms from high profile points on wear surfaces.